INST 262 (DCS and Fieldbus), section 2 Lab Automatically ...

Question 6
Examine this page of program code from a Siemens APOGEE system (written in Siemens’ “PPCL”
programming language), then answer the following questions:
02530 C
02540 C IF THE ROOM TEMP IS LESS THAN HEATING SETPOINT THAN TURN ON THE HEATING PUMP
02550 C ELSE SHUT OFF HEATING PUMP
02560 C
02570 IF ("MV.GH.2E:ROOM TEMP" .LT. "MV.GH.2E.HTG.STPT") THEN ON ("MV.GH.2E:DO 2")
02580 IF ("MV.GH.2E:ROOM TEMP" .GT. "MV.GH.2E.HTG.STPT"+1) THEN OFF ("MV.GH.2E:DO 2")
02590 C
02600 C *****ROOM 3E CONTROLS*****
02610 C
02620 C IF SOMEONE PUSHES THE OVERIDE BUTTON, THEN TURN ON THE EXHAUST FAN
02630 C OVERRIDE FOR 2 HOURS
02640 C
02650 IF ("MV.GH.3E:DI OVRD SW" .EQ. ON) THEN SET (0,"MV.GH.3E.OT")
02660 IF ("MV.GH.3E.OT" .GT. 1000) THEN SET (1000, "MV.GH.3E.OT")
02670 IF ("MV.GH.3E.OT" .LT. 120) THEN ON ("MV.GH.3E.OVRD") ELSE OFF ("MV.GH.3E.OVRD")
What is the significance of the letter C preceding many of the lines of code in this program?
Identify the meanings of the following “operators” in Siemens PPCL code: .LT., .GT., .EQ..
Explain how the “heating pump” code functions (lines 2570 and 2580) to turn the pump on and off.
Explain how the “exhaust fan override” code functions (lines 2650 and 2670) to turn the fan on for two
hours. Specifically, where does the code tell the Siemens controller to invoke a two-hour time delay?
Line 6000 of this program (not shown on this page) instructs the controller to GOTO 00190, with 00190
being a line near the beginning of the program (also not shown on this page). In fact, this is the only
“GOTO” instruction in the entire program. Why do you think this “GOTO” instruction exists?
Suggestions for Socratic discussion
• Do you think it would be easier or more difficult to program custom control algorithms in a text-based
language like PPCL or in a graphic-based language such as function blocks?
file i00671
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